Value of Tomosynthesis for the Detection of Sacro-iliitis (TOMOS SI)

Spondyloarthropathies (SpAs) are chronic inflammatory diseases encompassing ankylosing spondylitis, psoriatic arthritis, reactive arthritis, enteropathic arthropathy, and undifferentiated SpA. In 2001, the estimated prevalence of SpA was 1.5% worldwide. Sacroiliitis is a condition caused by inflammation within the sacroiliac joint. It is the most frequent damage of SpA depicted at imaging evaluation. Conventional radiography (X-ray) is usually used to depict the structural changes associated with sacroiliitis. However further evaluation often requires additionnal computed tomography (CT). Tomosynthesis is an Xray-based imaging technology which allows reconstruction of multiple section images from a set of projection images acquired as the x-ray tube moves along a prescribed path. The advantagee of tomosynthesis is the significant reduction of radiation dose exposure compared to CT Tomosynthesis is currently used in the field of breast imaging and pneumology. Very few studies have examined the value of tomosynthesis for osteoarticular imaging. The study aims at evaluating the diagnostic performances of tomosynthesis as compared to standard X-ray and CT, in patients with a clinical suspicion of sacroiliitis. the investigators hypothesize that tomosynthesis is superior to conventional radiography for detection of sacroiliitis and is at least equal to CT with lower irradiation.